1. Field of the Invention
The present invention relates to an apparatus and a method for decoding a channel code in a mobile communication system. More particularly, the present invention relates to an apparatus and a method for raising a data throughput by dynamically changing a maximum number of iterative decoding times of a channel code iteratively decodable in a mobile communication system.
2. Description of the Related Art
Mobile communications systems can raise data transmission efficiency by changing a data rate based on a channel condition using iteratively decodable codes such as turbo codes and Low Density Parity Check (LDPC) codes.
In the coding using the iterative decoding, the preset maximum number of iterative decoding times is important. The maximum number of the iterative decoding times is a factor in determining a decoding throughput of the entire system.
When determining that the output of a decoder is reliable prior to reaching the maximum number of the iterative decoding times during the data decoding process, the mobile communication system performs an early stopping algorithm which aborts the decoding process without decoding up to the maximum number of the iterative decoding times. The early stopping algorithm is explained in detail below with reference to FIGS. 1A and 1B.
FIG. 1A depicts a conventional frame structure of a mobile communication system.
The frame structure of FIG. 1A includes MAP information 110 and bursts 112. The MAP information 110, which is allocation information of the data bursts 112, includes information for determining the maximum number of the iterative decoding times of a frame. The MAP information 110 is contained at the head of the frame.
A receiver can acquire data on the current frame upon decoding the MAP information 110. Based on a decoding rate of the receiver, an upper bound of the number of the iterative decoding times can be calculated.
The burst 112 includes a plurality of Protocol Data Units (PDUs) 114. Each PDU 114 includes a MAC header 116 and may include a payload 118.
The MAC header 116 carries information relating to a size of the PDU 114. The size of the PDU 114 differs per PDU. The receiver can acquire the size of the payload 118 from the size of the PDU 114 of the MAC header 116. The payload 118 may include CRC information 120 for error checking.
The MAP information 110 delivers the MAP using a preset modulation scheme and a preset code rate. Alternatively, by dividing the MAP, the first MAP is transmitted using a preset modulation scheme and a preset code rate to inform of the modulation scheme and the code rate of a subsequent MAP.
The receiver decodes the frame by setting the maximum number of the iterative decoding times of the frame based on the MAP information 110 of the frame. When setting the maximum number of the iterative decoding times, the receiver needs to assume a worst case where the early stopping is not performed.
FIG. 1B depicts the conventional MAC header 116 of the PDU 114.
In the first row, the MAC header 116 of FIG. 1B includes a 1-bit HT field 130 indicative of a header type, a 1-bit EC field 132 indicative of encryption control, and a 6-bit Type field 134 indicative of a payload type. Herein, the HT field 130 of ‘0’ indicates a MAC header and ‘1’ indicates a band request header. The EC field 132 of ‘0’ indicates a non-encrypted payload and ‘1’ indicates an encrypted payload.
The first row of the general MAC header includes 1-bit reserved (Rsv) fields 136 and 142, a 1-bit CI field 138 indicative of the CRC check, a 2-bit EKS field 140 indicative of an encryption key sequence, and Most Significant Bit (MSB) 3 bits of a LEN field 144 indicative of a bytewise length of the MAC PDU including the MAC header. The second row of the general MAC header includes Least Significant Bit (LSB) 8 bits 146 of the LEN field and MSB 8 bits 150 of a CID field indicative of a Connection IDentifier (CID). The third row includes LSB 8 bits 148 of the CID field and an 8-bit HCS field 152 indicative of a header check sequence.
The receiver can determine whether the PDU is allocated to the receiver by checking the CID information of the MAC header and thereby may process to abort the decoding. Thus, the early stopping can be achieved by reducing the number of the iterative decoding times.
After determining the maximum number of the iterative decoding times using the MAP information, the receiver aborts the decoding according to the early stopping condition. Next, the receiver can determine whether to abort the decoding on the PDU based on the information (CID) of the MAC header and execute the early stopping and the decoding abortion based on the MAC header (CID) at the same time.
However, when the decoding is terminated before the scheduled time, the above-mentioned method cannot change the maximum number of the iterative decoding times in the frame. That is, when the decoding is completed earlier than scheduled, a demodulator is idle during the remaining time. Therefore, a conventional iterative decoding controller cannot attain sufficient iterative decoding gain.